[llvm-bugs] [Bug 34621] New: Support for saturated vector increment

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=34621

            Bug ID: 34621
           Summary: Support for saturated vector increment
           Product: libraries
           Version: 4.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm at henning-thielemann.de
                CC: llvm-bugs at lists.llvm.org

I have a special case of https://bugs.llvm.org/show_bug.cgi?id=14613 .
I add a vector to another vector but the first operand contains only zeros and
ones.

define <16 x i8> @increment_vector_sat(<16 x i8>, <16 x i8>) {
_L1:
  %v0 = and <16 x i8> %0, <i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8
1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1>
  %v1 = add <16 x i8> %v0, %1
  %b = icmp ult <16 x i8> %1, <i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1,
i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1>
  %v2 = select <16 x i1> %b, <16 x i8> %v1, <16 x i8> %1
  ret <16 x i8> %v2
}


$ opt-4.0 -O3 < bit-vector.ll | llc-4.0

        .section        .rodata.cst16,"aM", at progbits,16
        .p2align        4
.LCPI5_0:
        .zero   16,1
        .text
        .globl  increment_vector_sat
        .p2align        4, 0x90
        .type   increment_vector_sat, at function
increment_vector_sat:                   # @increment_vector_sat
# BB#0:                                 # %_L1
        pand    .LCPI5_0(%rip), %xmm0
        paddb   %xmm1, %xmm0
        pcmpeqd %xmm2, %xmm2
        pcmpeqb %xmm1, %xmm2
        por     %xmm2, %xmm0
        retq
.Lfunc_end5:
        .size   increment_vector_sat, .Lfunc_end5-increment_vector_sat


Could the X86 backend replace 'paddb' and the following code by a simple
'paddusb'?

An alternative would be a saturated add intrinsics.

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